DETECTOR BACKGROUNDS AT MUON COLLIDERS
TIPP 2011 ConferenceChicago
June 9-14, 2011
Nikolai Mokhov and Sergei Striganov
Fermilab
Fermilab Accelerator Physics Center
TIPP2011, Chicago, June 9-14, 2011
Outline
2Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
• Introduction
• Background Sources
• MDI and Background Load Modeling
• Main Characteristics of Backgrounds
Introduction
Physics goals of a Muon Collider (MC) can only be reached with appropriate design of the ring, interaction region (IR), high-field superconducting magnets, machine-detector interface (MDI) and detector. All - under demanding requirements, arising from the short muon lifetime, relatively large values of the transverse emittance and momentum spread, unprecedented dynamic heat loads (0.5-1 kW/m) and background particle rates in collider detector.TIPP2011, Chicago, June 9-14, 2011 3Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Muon Collider Parameters
Ecms TeV 1.5 4
frep Hz 15 6
nb 1 1
t s 10 27
N 1012 2 2
x,y m 25 25
L 1034 cm-2s-1 1 4
TIPP2011, Chicago, June 9-14, 2011 4Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
IR & Chromatic Correction Section
8-T dipoles in IR to generate large D at sextupoles to compensatechromaticity and sweep decay products; momentum acceptance 1.2%;dynamic aperture sufficient for transverse emittance of 50 m; under engineering constraints.Iterative studies on lattice and MDI with magnet experts:High-gradient (field) large-aperture short Nb3Sn quads and dipoles.TIPP2011, Chicago, June 9-14, 2011 5Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Sources of Background and Dynamic Heat Load
1. IP +- collisions: Production x-section 1.34 pb at √S = 1.5 TeV (negligible compared to #3).
2. IP incoherent e+e- pair production: x-section 10 mb which gives rise to background of 3×104 electron pairs per bunch crossing (manageable with nozzle & detector B)
3. Muon beam decays: Unavoidable bilateral detector irradiation by particle fluxes from beamline components and accelerator tunnel – major source at MC: For 0.75-TeV muon beam of 2x1012, 4.28x105 dec/m per bunch crossing, or 1.28x1010 dec/m/s for 2 beams; 0.5 kW/m.
4. Beam halo: Beam loss at limiting apertures; severe, can be taken care of by an appropriate collimation system far upstream of IP.
TIPP2011, Chicago, June 9-14, 2011 6Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
MARS15 Modeling
• Detailed magnet geometry, materials, magnetic fields maps, tunnel, soil outside and a simplified experimental hall plugged with a concrete wall.
• Detector model with Bz = 3.5 T and tungsten nozzle in a BCH2 shell, starting at ±6 cm from IP with R = 1 cm at this z.
• 750-GeV bunches of 2×1012 - and + approaching IP are forced to decay at |S| < Smax, where Smax up to 250 m at 4.28×105 / m rate, 1000 turns.
• Cutoff energies optimized for materials & particle types, varying from 2 GeV at ≥100 m to 0.025 eV (n) and 0.2 MeV (others) in the detector.
TIPP2011, Chicago, June 9-14, 2011 7Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Machine-Detector Interface
W
= 10o 6 < z < 600 cm x:z = 1:17
BCH2
Q1 = 5o
TIPP2011, Chicago, June 9-14, 2011 8Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Sophisticated shielding:W, iron, concrete & BCH2
Background Suppression
TIPP2011, Chicago, June 9-14, 2011 9Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Dipoles close to the IP and tungsten masks in each interconnect region help reduce background particle fluxes in the detector by a substantial factor. The tungsten nozzles, assisted by the detector solenoid field, trap most of the decay electrons created close to the IP as well as most of incoherent e+e- pairs generated in the IP. With additional MDI shielding, total reduction of background loads by more than three orders of magnitude is obtained.
Load to Detector: Two Nozzles
ParticleMinimal 0.6-
deg10-deg
Photon 1.5 x 1011 1.8 x 108
Electron 1.4 x 109 1.2 x 106
Muon 1.2 x 104 3.0 x 103
Neutron 5.8 x 108 4.3 x 107
Charged hadron
1.1 x 106 2.4 x 104
Number of particles per bunch crossing enteringdetector, starting from MARS source term for Smax=75m
0.6-deg
10-deg
X:Z=1:20No time cut applied, can help substantiallyAll results below are presented for 10-deg nozzle
TIPP2011, Chicago, June 9-14, 2011 10Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Where is Background Produced?Number of Particles Entering Detector
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 11
Where is Background Produced?Energy Flow Entering Detector
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 12
Energy Spectra Entering Detector
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 13
Time Distribution wrt Bunch crossing at Detector Entrance
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 14
Spatial Distribution at Detector Entrance
Most of particles come to detector through nozzle surface; for muons this fraction is 30%
Background (except muons) on nozzle surface weakly depends on azimuthal angle
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 15
+ beam
Muon Lateral Distribution at Detector Entrance
Positive muons deflected by beam-line magnetic field to negative direction
Negative muons deflected by beam-line magnetic field to positive direction
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov 16
Background Loads in Detector
TIPP2011, Chicago, June 9-14, 2011 17Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
Maximum neutron fluence and absorbed dose in the innermost layer of the silicon tracker for a one-year operation are at a 10% level of that in the LHC detectors at the luminosity of 1034 cm-2s-1
n
TIPP2011, Chicago, June 9-14, 2011
Summary
18Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
• A consistent IR lattice, which satisfies all the requirements from the beam dynamics point of view, has been designed for a 1.5-TeV muon collider with luminosity of 1034 cm-2s-1.
• Detector background simulations are advancing well, MDI optimization is underway, files are available to the community.
• Main features of background loads on the detector have been studied and are well understood.
• Detector physics modeling in presence of the machine backgrounds has been started and progressing very well.
TIPP2011, Chicago, June 9-14, 2011 Detector Backgrounds at Muon Colliders - N. Mokhov, S. Striganov
19
μ+μ- →γ*/Z0 events“detectable” energy – 1300 GeV
Energy spectra in tracker (+-46x46x5cm) with and without tungsten shielding
Nozzle geometry in MARS
Standard 10 degree nozzle New nozzle
Comparison new and old shielding
Tungsten radiation length – 0.35 cm
Tungsten nuclear interaction length – 10 cm.
10 cm tungsten -29 gamma/electron
interactions.
10 cm tungsten – 1 proton/neutron interaction.
Ratio new/old shielding
===============================
number energy
Gamma 26 28
Positron 14 8
Electron 26 15
Muon 38 3.5
Neutron 3.2 2.2
Ch hadron 2.5 2.8